24 FORESTRY 



x 

 and the white pine which is proving one of the best trees 



for planting in Germany. But in these cases the amount 



of heat is very similar in each locality and there is no real 



change in the demands of the species itself. 



The local range of a species is affected by heat, chiefly 

 in a mountainous country not only through altitude, but by 

 the difference in the exposure on slopes facing to different 

 points of the compass. A south or southwest slope is much 

 warmer than a north or northeast exposure. Toward the 

 northern portion of its range, a species will favor south 

 slopes and low altitudes while at the southern limit it will 

 only be found on the north slopes and toward the tops of 

 the mountains. 



Examples of such distribution are found in the pines of 

 the United States. The white pine is normally limited to 

 the Lake States, Pennsylvania and New England, but in the 

 Appalachian range it extends southward into North Caro- 

 lina where on the high summits of the great Smoky Moun- 

 tains at 5,000 feet elevation it comprises over 50 per cent 

 of the stand in some places. On the other hand even the 

 most hardy of the southern yellow pines, the shortleaf, con- 

 fines itself to the plains and foothills, and is never found 

 further north than New Jersey, while the longleaf pine 

 is found largely below Virginia, and its cousin, the Cuban 

 pine, is only met with along the gulf coast. 



Soil Moisture and its Relation to the Life of Trees. — 

 While heat fixes the general range of a tree, the demand 

 for moisture in the soil has a far greater influence locally 

 in determining which of several different species will sur- 

 vive in a struggle. Water in the soil not only enables the 

 tree to dissolve, with the aid of weak solutions of acids, 

 the plant food it needs, and absorb it by osmosis into the 

 root cells, from which it is slowly conducted upward until 

 it finally reaches the leaves, but it is vitally necessary to 

 the existence and functions of the leaves themselves. The 

 constant supply of water makes good the loss by transpira- 



